TWI575334B - Inspection method, lithographic apparatus, mask and substrate - Google Patents

Description

Inspection method, lithography device, reticle and substrate

This invention relates to inspection methods that can be used, for example, in the fabrication of devices by lithography.

A lithography apparatus is a machine that applies a desired pattern onto a substrate, typically applied to a target portion of the substrate. The lithography apparatus can be used, for example, in the fabrication of integrated circuits (ICs). In that case, a patterned device (which is alternatively referred to as a reticle or a proportional reticle) can be used to create a circuit pattern to be formed on individual layers of the IC. This pattern can be transferred onto a target portion (eg, a portion containing a die, a die, or a plurality of dies) on a substrate (eg, a germanium wafer). Transfer of the pattern is typically performed via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of sequentially adjacent adjacent target portions. Known lithography apparatus includes a so-called stepper in which each target portion is irradiated by exposing the entire pattern to a target portion at a time; and a so-called scanner in which a given direction ("scanning" direction) Each of the target portions is irradiated by scanning the pattern via the radiation beam while scanning the substrate in parallel or anti-parallel in this direction. It is also possible to transfer the pattern from the patterned device to the substrate by imprinting the pattern onto the substrate.

To monitor the lithography program, one or more parameters of the patterned substrate are measured. For example, such parameters can include overlay errors between sequential layers formed in or on the patterned substrate, and/or critical linewidths of the developed photosensitive resist. Can be on the product substrate and / or Perform this measurement on a dedicated metrology target. There are various techniques for performing measurements of microstructures formed in lithography procedures, including the use of scanning electron microscopes and various other specialized tools. A specialized inspection tool in a fast and non-invasive form is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and one or more properties of the scattered or reflected beam are measured. The properties of the substrate can be determined by comparing one or more properties of the beam before and after it has been reflected or scattered by the substrate. For example, this determination can be made by comparing the reflected beam to data stored in a known measurement library associated with one or more known substrate properties. Two main types of scatterometers are known to us. A spectral scatterometer directs a broadband radiation beam onto a substrate and measures the spectrum of the radiation (intensity that varies according to wavelength) that is scattered into a particular narrow range of angles. The angular resolution scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

Focus measurement in EUV lithography can be based on changes in focus calibration marks on the substrate via different focus settings. U.S. Patent Application Publication No. US 2009-0135398 discloses a phase grating alignment sensor that can be used to read the indicia. The size of the focus calibration mark read using the method disclosed in the document is 600 x 600 square microns. The method used to measure the focus in EUV lithography is based on the detection of mark quality changes via focus and is extremely sensitive to dose and program changes.

In order to use a scatterometer for focus readout, the target should be small (eg, 40 x 40 square microns) to meet customer requirements such as target area, and the number of line spaces within the beamwidth of the metrology tool should be more than 10 Cycles. The method of using the scatterometer for focus measurement can be based on the measurement of the critical dimension (CD) and sidewall angle (SWA) of the target (eg, periodic structure (grating) on the substrate).

However, this diffraction-based metrology method does not work so well for EUV device fabrication procedures for a variety of reasons. In particular, the EUV resist film thickness is significantly lower than the 193 nm infiltrated lithography EUV resist film thickness (~100 nm) (~50) Nano and below), this situation makes it difficult to extract accurate SWA and/or CD information from the EUV substrate.

For example, it would be desirable to provide a method that enables the use of diffraction-based metrology in structures exposed using an EUV system.

According to one aspect, a method of obtaining focus information associated with a lithography program is provided, the method comprising: providing at least one target comprising an alternating first structure and a second structure, the second structure being in the form The focus is dependent such that its form depends on the focus of the patterned beam used to form one of the targets, and the forms of the first structures do not have the same focus dependence as the focus of the second structures; And detecting an amount of radiation that is scattered by the target to obtain an asymmetry measure indicative of an overall asymmetry of the target for the target, wherein the asymmetry measure indicates the pattern when the target is formed This focus of the beam.

According to one aspect, a reticle is provided, comprising: a pattern for patterning a light beam to form a target, the target comprising alternating first and second structures, the reticle comprising for forming the first a first structural feature of the structure and a second structural feature for forming the second structure, wherein the second structural features are configured such that the forms of the second structure are focus dependent such that the form is dependent on a focus of the patterned beam at the time the object is formed, and the first structural features are configured such that the forms of the first structures do not have the same focus dependence as the focus of the second structures .

According to one aspect, a substrate is provided that includes a target having alternating first and second structures, wherein: both the first structure and the second structure comprise a low resolution substructure; The second structure includes one or more high resolution substructures whose number and/or size of high resolution substructures has been determined by forming a focus of the patterned beam of one of the targets.

2‧‧‧Broadband radiation projector/radiation source

4‧‧‧Spectrometer detector

10‧‧‧Spectrum

11‧‧‧Backward projection aperture plane

12‧‧‧Lens system

13‧‧‧Interference filter

14‧‧‧Refer to the mirror

15‧‧‧Microscope lens/lens system

16‧‧‧Partial reflective surface/beam splitter

17‧‧‧ polarizer

18‧‧‧Detector

30‧‧‧Substrate target

502‧‧‧Steps

503‧‧‧Steps

504‧‧‧Steps

506‧‧‧Steps

508‧‧‧Steps

510‧‧ steps

512‧‧‧Steps

514‧‧‧Steps

602‧‧ steps

603‧‧‧Steps

604‧‧‧Steps

606‧‧‧Steps

608‧‧‧Steps

610‧‧‧Steps

612‧‧ steps

614‧‧‧Steps

616‧‧‧Steps

700‧‧‧Interlaced scatterometer stack target

705‧‧‧ first structure

710‧‧‧Second structure

715‧‧‧Diffraction-based focus (DBF) target

720‧‧‧Diffraction-based focus (DBF) structure

725‧‧‧High-resolution substructure/high resolution features

730‧‧‧ revised target

730'‧‧‧ Target

740‧‧‧first goal

750‧‧‧second target/second structure

760‧‧‧High-resolution substructure

770‧‧‧Low-resolution substructure

775‧‧‧ first structure

810‧‧‧ first structure

810'‧‧‧ first structure

850‧‧‧Second structure

850'‧‧‧Second structure

850"‧‧‧ second structure

860‧‧‧High-resolution substructure

860'‧‧‧ horizontal substructure

860"‧‧‧substructure

870‧‧‧Low-resolution substructure

880‧‧‧High-resolution substructure

890‧‧‧Low-resolution substructure

900‧‧‧ Target

910‧‧‧ Target

910'‧‧‧ Target

920‧‧‧ Target

920'‧‧‧ Target

930‧‧‧ Target

930'‧‧‧ Target

950a‧‧‧Second structure

950b‧‧‧Second structure

950c‧‧‧Second structure

950d‧‧‧second structure

960‧‧‧High-resolution substructure

1040‧‧‧ first structure

1060‧‧‧First effective structure

1060c‧‧‧second effective structure

1100‧‧‧Plotting

1110‧‧‧ District

1200‧‧‧Interlaced target design/goal

1210‧‧‧ first structure

1220‧‧‧Second structure

1230‧‧‧ Interwoven targets

1240‧‧‧Fourth structure

1250‧‧‧ third structure

1310‧‧‧ Curve

Line 1320‧‧

1330‧‧‧Curve/Asymmetric Signal

1340‧‧‧ Curve

1350‧‧‧Asymmetric line content/asymmetry signal

1360‧‧‧Focus response curve/signal

1400‧‧‧ patterned devices

1400'‧‧‧ patterned devices

1405‧‧‧Main product area

1410‧‧‧Cutting area/cutting area

1415‧‧‧Second structure

1415'‧‧‧Second structure

1420‧‧‧ structure

1425‧‧‧First structure

1425'‧‧‧ first structure

1430‧‧‧ Structure

1440‧‧‧Overlapping area

1445‧‧‧Printed structure

AD‧‧‧ adjuster

B‧‧‧radiation beam

BD‧‧•beam delivery system

BK‧‧· baking sheet

C‧‧‧Target section

CH‧‧‧Cooling plate

CO‧‧‧ concentrator

DE‧‧‧developer

IF‧‧‧ position sensor

IL‧‧‧Lighting system/illuminator

IN‧‧‧ concentrator

I/O1‧‧‧Input/Output埠

I/O2‧‧‧Input/Output埠

LA‧‧‧ lithography device

LACU‧‧‧ lithography control unit

LB‧‧‧Loader

LC‧‧‧ lithography manufacturing unit

M ₁ ‧‧‧ patterned device alignment mark

M ₂ ‧‧‧ patterned device alignment mark

MA‧‧‧patterned device

MT‧‧‧Support structure

P ₁ ‧‧‧Substrate alignment mark

P ₂ ‧‧‧Substrate alignment mark

PM‧‧‧First Positioner

PL‧‧‧Projection System

PU‧‧‧Processing unit

PW‧‧‧Second positioner

RO‧‧‧Substrate handler or robot

SC‧‧‧Spin coater

SCS‧‧‧Supervisory Control System

SO‧‧‧radiation source

TCU‧‧‧ Coating Development System Control Unit

W‧‧‧Substrate

WTa‧‧‧ substrate table

WTb‧‧‧ substrate table

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which Figure 1 schematically depicts a lithography apparatus; Figure 2 schematically depicts a lithographic cell or cluster; Figure 3 schematically depicts a first scatterometer; Figure 4 schematically depicts a second scatter Figure 5 depicts an example program for re-constructing a structure for self-scattering metrology; Figure 6 depicts another example procedure for re-constructing a structure for self-scattering metrology; Figure 7a schematically depicts an interleaved stack Figure 7b schematically depicts a diffraction based focus (DBF) measurement target; Figure 7c schematically depicts an object in accordance with an embodiment of the present invention; Figure 7d schematically depicts this The object of an additional embodiment of the invention; FIG. 8 schematically depicts details of an alternative target configuration in accordance with further embodiments of the present invention; FIG. 9 schematically depicts several targets that have been exposed with different focus settings; FIG. Schematically depicting the details of the two targets exposed with (a) the best focus and (b) the exposure with defocus, and the approximation of the rayometer to detect the matter; Figure 11 is the y-axis Symmetry or center of gravity and focus on the x-axis a plot to illustrate how to obtain focus sign information; and FIG. 12 shows a dual target configuration for extracting focus sign information in accordance with an embodiment of the present invention; FIGS. 13a-13b show the same for FIG. Asymmetry signal amplitude (y-axis) of two targets (including its component signals) versus the focus (x-axis), and Figure 13c shows the determination of the difference between the graphs of Figures 13a to 13b; and Figure 14a And Figure 14b illustrates the generation of the first set of structures and the second set of structures in two separate exposures without the need for a second patterned device or a second patterned device pattern. law.

Figure 1 schematically depicts a lithography apparatus. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (eg, UV radiation or DUV radiation), and a support structure (eg, a reticle stage) MT configured to support the patterned device (eg, reticle) MA, and connected to a first locator PM configured to accurately position the patterned device according to certain parameters; a substrate table (eg, wafer table) WT that is constructed to hold a substrate (eg, a resist coated wafer) W and coupled to a second locator PW configured to accurately position the substrate according to certain parameters; and a projection system (eg, a refractive projection lens system) PL It is configured to project a pattern imparted by the patterned device MA to the radiation beam B onto a target portion C of the substrate W (eg, comprising one or more dies).

The illumination system can include various types of optical components for guiding, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

The support structure holds the patterned device in a manner that depends on the orientation of the patterned device, the design of the lithography device, and other conditions, such as whether the patterned device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterned device. The support structure can be, for example, a frame or table that can be fixed or movable as desired. The support structure ensures that the patterned device is, for example, in a desired position relative to the projection system. Any use of the terms "proportional mask" or "reticle" herein is considered synonymous with the more general term "patterned device."

The term "patterned device" as used herein shall be interpreted broadly to mean that a pattern can be imparted to a radiation beam in a cross section of a radiation beam for the target portion of the substrate. Any device that produces a pattern. It should be noted that, for example, if the pattern imparted to the radiation beam includes a phase shifting feature or a so-called auxiliary feature, the pattern may not exactly correspond to the desired pattern in the target portion of the substrate. Typically, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device (such as an integrated circuit) produced in the target portion.

The patterned device can be transmissive or reflective. Examples of patterned devices include photomasks, programmable mirror arrays, and programmable LCD panels. Photomasks are well known in lithography and include reticle types such as binary, alternating phase shift and attenuated phase shift, as well as various hybrid reticle types. One example of a programmable mirror array uses a matrix configuration of small mirrors, each of which can be individually tilted to reflect the incident radiation beam in different directions. The tilted mirror imparts a pattern in the radiation beam reflected by the mirror matrix.

The term "projection system" as used herein shall be interpreted broadly to encompass any type of projection system suitable for the exposure radiation used or other factors such as the use of a immersion liquid or the use of a vacuum, including refraction, reflection. , catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein is considered synonymous with the more general term "projection system."

As depicted herein, the device is of the transmissive type (eg, using a transmissive reticle). Alternatively, the device may be of a reflective type (eg, using a programmable mirror array of the type mentioned above, or using a reflective mask).

The lithography apparatus may have two (dual stage) or more than two stages (for example, two or more substrate stages and/or two or more patterned device stages, and/or a substrate stage) And the type of the substrate that does not hold the substrate. In such "multi-stage" machines, additional stations may be used in parallel, or preliminary steps may be performed on one or more stations while one or more other stations are used for exposure.

The lithography apparatus can also be of the type wherein at least a portion of the substrate can be covered by a liquid (eg, water) having a relatively high refractive index to fill the space between the projection system and the substrate. The infiltrating liquid can also be applied to other spaces in the lithography apparatus, for example, a reticle The space between the projection system and the projection system. Infiltration techniques are well known in the art for increasing the numerical aperture of a projection system. The term "wetting" as used herein does not mean that a structure such as a substrate must be immersed in a liquid, but rather only means that the liquid is located between the projection system and the substrate during exposure.

Referring to Figure 1, illuminator IL receives a radiation beam from radiation source SO. For example, when the radiation source is a quasi-molecular laser, the radiation source and the lithography device can be separate entities. Under such conditions, the radiation source is not considered to form part of the lithography apparatus, and the radiation beam is transmitted from the radiation source SO to the illuminator IL by means of a beam delivery system BD comprising, for example, a suitable guiding mirror and/or beam expander. . In other cases, for example, when the source of radiation is a mercury lamp, the source of radiation may be an integral part of the lithography apparatus. The radiation source SO and illuminator IL together with the beam delivery system BD (when needed) may be referred to as a radiation system.

The illuminator IL can include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. In general, at least the outer radial extent and/or the inner radial extent (commonly referred to as σ outer and σ inner, respectively) of the intensity distribution in the pupil plane of the illuminator can be adjusted. Additionally, the illuminator IL can include various other components such as the concentrator IN and the concentrator CO. The illuminator can be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross section.

The radiation beam B is incident on a patterned device (e.g., reticle) MA that is held on a support structure (e.g., a reticle stage) MT, and is patterned by the patterned device. In the case where the patterned device MA has been traversed, the radiation beam B is transmitted through the projection system PL, which projects the beam onto the target portion C of the substrate W. With the second positioner PW and the position sensor IF (for example, an interference measuring device, a linear encoder, a 2D encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example, to make different target portions C Positioned in the path of the radiation beam B. Similarly, the first locator PM and another position sensor (which is not explicitly depicted in FIG. 1) can be used, for example, after mechanical scooping from the reticle library or during scanning relative to the radiation beam The path of B to accurately position the patterned device MA. In general, a long stroke module that can form a component of the first positioner PM (rough positioning) and short stroke module (fine positioning) to achieve the movement of the support structure MT. Similarly, the movement of the substrate table WT can be achieved using a long stroke module and a short stroke module that form the components of the second positioner PW. In the case of a stepper (relative to the scanner), the support structure MT can be connected only to the short-stroke actuator or can be fixed. The patterned device MA and the substrate W can be aligned using the patterned device alignment marks M1, M2 and the substrate alignment marks P1, P2. Although the illustrated substrate alignment marks occupy dedicated target portions, the marks may be located in the space between the target portions (the marks are referred to as scribe line alignment marks). Similarly, where more than one die is provided on the patterned device MA, the patterned device alignment mark can be located between the dies.

The depicted device can be used in at least one of the following modes:

1. In the step mode, the support structure MT and the substrate table WT are kept substantially stationary (i.e., a single static exposure) while the entire pattern to be imparted to the radiation beam is projected onto the target portion C at a time. Next, the substrate stage WT is displaced in the X and/or Y direction so that different target portions C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C of the image in a single static exposure.

2. In the scan mode, when the pattern to be given to the radiation beam is projected onto the target portion C, the support structure MT and the substrate stage WT (i.e., single dynamic exposure) are synchronously scanned. The speed and direction of the substrate stage WT relative to the support structure MT can be determined by the magnification (reduction ratio) and image inversion characteristics of the projection system PL. In the scan mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), and the length of the scanning motion determines the length of the target portion (in the scanning direction).

3. In another mode, the support structure MT is held substantially stationary while the pattern to be imparted to the radiation beam is projected onto the target portion C, thereby holding the programmable patterning device and moving or scanning the substrate table WT . In this mode, a pulsed radiation source is typically used, and the programmable patterning device is updated as needed between each movement of the substrate table WT or between successive pulses of radiation during a scan. This mode of operation can be easily applied A reticle lithography that utilizes a programmable patterning device, such as a programmable mirror array of the type mentioned above.

Combinations of the modes of use described above and/or variations or completely different modes of use may also be used.

As shown in FIG. 2, the lithography apparatus LA forms a component of a lithography fabrication unit LC (sometimes referred to as a cluster), and the lithography fabrication unit LC also includes means for performing a pre-exposure procedure and a post-exposure procedure on the substrate. Typically, such devices include one or more spin coaters SC for depositing a resist layer, one or more developers DE to develop an exposed resist, one or more cooling plates CH, and/or One or more baking sheets BK. The substrate handler or robot RO picks up the substrate from the input/output ports I/O1, I/O2, moves the substrate between different program devices, and delivers the substrate to the load port LB of the lithography device. These devices, often collectively referred to as coating development systems, are under the control of the coating development system control unit TCU, and the coating development system control unit TCU itself is controlled by the supervisory control system SCS, and the supervisory control system SCS is also The lithography device is controlled via a lithography control unit LACU. Thus, different devices can be operated to maximize yield and processing efficiency.

In order to properly and consistently expose the substrate exposed by the lithography apparatus, it is necessary to inspect the exposed substrate to measure properties such as overlay error, line thickness, critical dimension (CD), and the like between subsequent layers. If an error is detected, the exposure of the subsequent substrate can be adjusted, especially if the inspection can be performed quickly enough and quickly such that one or more of the other substrates of the same batch are still to be exposed. Also, the exposed substrate can be stripped and reworked - to improve yield - or the exposed substrate can be discarded, thereby avoiding exposure to known defective substrates. In the event that only some of the target portions of the substrate are defective, additional exposure may be performed only for good target portions.

An inspection device is used to determine the properties of the substrate, and in particular to determine how one or more of the different layers of the different substrates or the same substrate vary between layers. The inspection device can be integrated into the lithography device LA or the lithography manufacturing unit LC, or can be a stand-alone device. In order to achieve For the fastest measurement, it is necessary to have the inspection device immediately after exposure to measure the properties in the exposed resist layer. However, the latent image in the resist has a very low contrast - there is only a very small difference in refractive index between the portion of the resist that has been exposed to radiation and the portion of the resist that has not been exposed to radiation - and not all The inspection device is sufficiently sensitive to measure the amount of latent image. Therefore, the measurement can be taken after the post-exposure bake step (PEB), which is usually the first step of the exposed substrate and increases the exposed portion and the unexposed portion of the resist. The contrast between. At this stage, the image in the resist can be referred to as a semi-latent. It is also possible to perform a measurement of the developed resist image - at this point, the exposed or unexposed portion of the resist has been removed - or after development of a pattern transfer step such as etching Measurement of the etchant image. The latter possibility limits the possibility of reworked defective substrates, but still provides useful information.

Figure 3 depicts a scatterometer that can be used in one embodiment of the invention. The scatterometer includes a broadband (white light) radiation projector 2 that projects radiation onto a substrate W. The reflected radiation is transmitted to the spectrometer detector 4, which measures the spectrum 10 of the specularly reflected radiation (intensity that varies depending on the wavelength). From this data, the processing unit PU can reconstruct the structure or profile that causes the detected spectrum, for example, by tightly coupled wave analysis and nonlinear regression, or by comparison with the simulated spectral library shown at the bottom of Figure 3. . In general, for reconstruction, the general form of the structure is known to us, and the knowledge of the procedure for manufacturing the structure is assumed to assume some parameters, leaving only a few parameters of the structure to be determined from the self-scattering measurement data. This scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

Another scatterometer that can be used is shown in FIG. In this device, the radiation emitted by the radiation source 2 is collimated using the lens system 12 and transmitted through the interference filter 13 and the polarizer 17, reflected by the partially reflective surface 16 and focused to the substrate W via the microscope objective lens 15. Above, the microscope objective 15 has a high numerical aperture (NA), desirably at least 0.9 or at least 0.95. The infiltrant scatterometer can even have a lens with a numerical aperture greater than one. The reflected radiation is then transmitted through the partially reflective surface 16 to the detector 18 to cause the scattered spectrum to be detected. The detector may be located in the back projection aperture plane 11 and the back projection aperture plane 11 is at the focal length of the lens system 15, however, the pupil plane may instead use auxiliary optics (not shown) And then imaged to the detector. The pupil plane defines the plane of incidence for the radial position of the radiation and the plane of the angle defines the azimuth of the radiation. The detector is desirably a two-dimensional detector such that the two-dimensional angular scattering spectrum of the substrate target 30 can be measured. The detector 18 can be, for example, a CCD or CMOS sensor array, and can use, for example, an integration time of 40 milliseconds per frame.

The reference beam is often used, for example, to measure the intensity of incident radiation. To perform this measurement, when the radiation beam is incident on the beam splitter 16, a portion of the radiation beam is transmitted through the beam splitter as a reference beam toward the reference mirror 14. The reference beam is then projected onto different portions of the same detector 18 or alternatively onto different detectors (not shown).

The set of interference filters 13 can be used to select a wavelength of interest in the range of, for example, 405 nm to 790 nm or even lower (such as 200 nm to 300 nm). The interference filter can be tunable rather than containing a collection of different filters. A grating can be used instead of the interference filter.

Detector 18 measures the intensity of the scattered radiation at a single wavelength (or narrow wavelength range), the intensity of the scattered radiation at multiple wavelengths, or the intensity of the scattered radiation integrated over a range of wavelengths. In addition, the detector can separately measure the intensity of the transverse magnetic polarization radiation and the lateral electrical polarization radiation, and/or the phase difference between the transverse magnetic polarization radiation and the lateral electrical polarization radiation.

It is possible to use a broadband radiation source (i.e., a radiation source having a wide radiation frequency or range of wavelengths and thus a wide range of colors), which gives a large etendue, allowing mixing of multiple wavelengths. The plurality of wavelengths in the wide band desirably each have a bandwidth of Δλ and an interval of at least 2 Δλ (that is, twice the bandwidth). A number of "sources" of radiation may be different portions of an extended source of radiation that have been split using fiber bundles. In this way, The angular resolution scattering spectra are measured in parallel at multiple wavelengths. The 3-D spectrum (wavelength and two different angles) can be measured, which contains more information than the 2-D spectrum. This situation allows for more information to be measured, which increases the stability of the metrology program. This situation is described in more detail in European Patent Application Publication No. EP1628164, which is incorporated herein by reference.

The target 30 on the substrate W can be a 1-D grating that is printed such that after development, the bars are formed from solid resist lines. Target 30 can be a 2-D grating that is printed such that after development, the grating is formed from solid resist pillars or vias in the resist. The rod, pillar or via may alternatively be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and the illumination symmetry and the presence of this aberration will manifest itself as a change in the printed raster. Therefore, the scattering measurement data of the printed grating is used to reconstruct the grating. Parameters of the 1-D grating (such as line width and shape) or parameters of the 2-D grating (such as pillar or via width or length or shape) may be input to the self-printing step by the processing unit PU and/or other Reconstruction procedures performed by knowledge of the scatterometry program.

As described above, the target is on the surface of the substrate. This goal will often take the shape of one of the series of lines in the grating or the shape of a substantially rectangular structure in the 2-D array. The purpose of the rigorous optical diffraction theory in metrology is to efficiently calculate the diffraction spectrum from the target reflection. In other words, the target shape information for critical dimension (CD) uniformity and stacking weights and measures is obtained. The stack-to-weight measure is a measure that measures the stack of two targets to determine if the two layers on the substrate are aligned. CD uniformity is simply a measure of the uniformity of the grating on the spectrum used to determine how the exposure system of the lithography apparatus operates. In particular, the CD or critical dimension is the width of the object "written" on the substrate and is the limit at which the lithographic apparatus can be physically written on the substrate.

In the case where one of the scatterometers described above is used in conjunction with a model of the target structure such as target 30 and its diffraction properties, the shape of the structure and the measurement of other parameters can be performed in a number of ways. In the first type of program represented by Figure 5, the calculation is based on the purpose A first estimated diffraction pattern of the target shape (first candidate structure) and comparing the diffraction pattern to the observed diffraction pattern. The parameters of the model are then systematically varied and the diffraction is recalculated in a series of iterations to generate new candidate structures and thus achieve a best fit. In the second type of program represented by Figure 6, the diffraction spectra for a number of different candidate structures are pre-calculated to produce a diffraction spectrum "library." Next, compare the diffraction pattern of the self-measured target observation with the calculated spectral library to find the best fit. Two methods can be used together: a rough fit can be obtained from the library, followed by a repeat procedure to find the best fit.

Referring in more detail to Figure 5, the manner in which the target shape and/or material properties are measured will be generally described. For this description, it will be assumed that the target is periodic (1-D structure) in only one direction. In practice, it can be periodic (2- or 3-dimensional structure) in 2 or 3 directions and will be adapted accordingly.

At 502, scatterometers, such as the scatterometers described above, are used to measure the diffraction pattern of the actual target on the substrate. This measurement diffraction pattern is forwarded to a computer such as a computer calculation system. The algorithm may be the processing unit PU mentioned above, or it may be a separate device.

At 503, a "model recipe" is established that defines a parametric model of the target structure based on a number of parameters p _i (p ₁ , p ₂ , p _{3 ,} etc.). In a 1-D periodic structure, such parameters may represent, for example, the angle of the sidewall, the height or depth of the feature, and/or the width of the feature. The target material and one or more of the underlying properties are also represented by parameters such as refractive index (at a particular wavelength present in the scatter radiation beam). Specific examples will be given below. Significantly, although the target structure can be defined by many parameters describing its shape and material properties, for the purposes of the following program steps, the model recipe defines many of these parameters as having a fixed value, while other parameters will be variable. Or "floating" parameters. The procedure for selecting between fixed and floating parameters is described below. In addition, a way to permit parameter changes rather than completely non-dependent floating parameters will be introduced. For the purposes of describing Figure 5, only the variable parameters are considered to be the parameter pi.

At 504, the model target shape is estimated by setting an initial value p _i ⁽⁰⁾ for the floating parameter (ie, P ₁ ⁽⁰⁾ , P ₂ ⁽⁰⁾ , P ₃ ^(0), etc.). Each floating parameter will be generated within a predetermined range as defined in the recipe.

At 506, one or more different parameters representing the estimated shape, along with different elements of the model, are used, for example, using a rigorous optical diffraction method such as RCWA or any other solver of Maxwell's equations. Optical properties to calculate one or more scattering properties. This calculation gives an estimated or model diffraction pattern of the estimated target shape.

At 508, 510, the diffraction pattern and the model diffraction pattern are then compared and the similarity and/or difference between the measurement diffraction pattern and the model diffraction pattern is used to calculate a "quality function" for the model target shape.

At 512, one or more new parameters P ₁ ⁽¹⁾ , P ₂ ⁽¹⁾ , P ₃ ^{(1 ) are} estimated assuming that the quality function indicates that the model needs to be improved before it accurately represents the actual target shape. ^And so on and the one or more new parameters are repeatedly fed back into step 506. Steps 506 through 512 are repeated.

To aid in the search, the calculus in step 506 may further generate a partial derivative of the quality function in this particular region of the parameter space, which indicates that increasing or decreasing the parameter will increase or decrease the sensitivity of the quality function. The calculation of the quality function and the use of the derivative are generally known in the art and will not be described in detail herein.

At 514, when the quality function indicates that the repeated procedure has converge to a solution with the desired accuracy, one or more of the currently estimated parameters are reported as measurements of the actual target structure.

The computation time of this iterative procedure is primarily determined by the previous diffraction model used, that is, the estimated model diffraction pattern is calculated from the estimated target structure using the rigorous optical diffraction theory. If more parameters are needed, there is more freedom. The calculus time increases in principle with the power of the number of degrees of freedom. The estimated or model diffraction pattern calculated at 506 can be expressed in various forms. If the calculated pattern is expressed in the same form as the measurement pattern generated in step 502, the comparison is simplified. For example, the model can be easily compared The characterized spectrum is compared to the spectrum measured by the apparatus of Figure 3; the patterned pupil pattern and the pupil pattern measured by the apparatus of Figure 4 can be easily compared.

Throughout this description from Figure 5, the term "diffraction pattern" will be used assuming the scatterometer of Figure 4 is used. Those skilled in the art can readily adapt the teaching to different types of scatterometers, or even to other types of measuring instruments.

6 illustrates an additional example program in which a plurality of model diffraction patterns for different estimated target shapes (candidate structures) are pre-calculated, and the plurality of model diffraction patterns are stored in a library for actual measurement Comparison. The basic principles and terminology are the same as the basic principles and terminology for the procedure of Figure 5. The procedure of the procedure of Figure 6 is: at 602, the process of generating the library begins. A separate library can be generated for each type of target structure. The library may be generated by a user of the measurement device as needed, or may be pre-generated by a supplier of the device.

At 603, a "model recipe" is established that defines a parametric model of the target structure based on a number of parameters p _i (p ₁ , p ₂ , p _{3 ,} etc.). The considerations are similar to the considerations in step 503 of the repeated procedure.

At 604, the parameters are generated, for example, by generating a random value for each of the first set of parameters P ₁ ⁽⁰⁾ , P ₂ ⁽⁰⁾ , P ₃ ^(0), etc., each random The value is within the expected range of values for this parameter set.

At 606, the calculus model diffracts the pattern and stores the model diffraction pattern in a library that represents a diffraction pattern that is expected from a target shape that is free of one or more parameter representations.

At 608, a new set of shape parameters p ₁ ⁽¹⁾ , p ₂ ⁽¹⁾ , p ₃ ^(1), and the like are generated. Steps 606 through 608 are repeated dozens of times, hundreds of times, or even thousands of times until the library containing all of the stored modeled diffraction patterns is judged to be sufficiently complete. Each stored pattern represents one of the sample points in the multidimensional parameter space. The samples in the library should be filled into the sample space with sufficient density so that any actual diffraction pattern will be represented close enough.

At 610, after the library is generated (but before the library is generated), the actual target 30 is placed in the scatterometer and the diffraction pattern of the actual target 30 is measured.

At 612, the assay pattern is compared to one or more modeled patterns stored in the library to find the best match pattern. This comparison can be made with each sample in the library, or a more systematic search strategy can be used to reduce the computational burden.

At 614, if a match is found, the estimated target shape used to generate the matching library pattern can be determined to approximate the object structure. The output corresponds to one or more shape parameters of the matching sample as one or more measured shape parameters. A matching procedure can be performed directly on the model diffracted signal, or a matching procedure can be performed on the surrogate model that is optimized for rapid evaluation.

At 616, the closest matching sample is used as a starting point, as appropriate, and an improved procedure is used to obtain one or more final parameters for reporting. For example, the improved program can include a repetitive procedure that is very similar to the repeated procedure shown in FIG.

Whether or not to use the improvement step 616 depends on the choice of the implementer. If the library is sampled intensively, it is not necessary to improve it because a good match can always be found. On the other hand, this library may be too large to be used for practice. Thus, a practical solution uses a library search for a coarse set of parameters, followed by a quality function that is repeated one or more times to determine a more accurate set of parameters to report the set of parameters of the target substrate with the desired accuracy. In the case of performing an additional iteration, adding the calculated diffraction pattern and the associated improved parameter set as new inputs to the library will be an option. In this manner, a library that is built into a larger library based on a relatively small amount of computational effort but with the computational effort of the improved step 616 can be initially used. Regardless of which scheme is used, further improvements in the value of one or more of the reported variable parameters may be obtained based on the goodness of fit of the plurality of candidate structures. For example, a final set of parameter values can be generated by interpolating between parameter values of two or more candidate structures, which assumes that both or all of their candidate structures have a high match. Minute.

The calculation time of this repeated procedure is mainly by the previous diffraction at steps 506 and 606. The model determines, that is, the estimated model diffraction pattern is calculated from the estimated target shape using the rigorous optical diffraction theory.

As the dimensions of features fabricated using lithography become smaller and smaller, lithography is becoming a more decisive factor for enabling the fabrication of small ICs or other devices and/or structures. The theoretical estimation of the pattern printing limit can be given by the Rayleigh resolution criterion, as shown by equation (1):

Where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k ₁ is the program dependent adjustment factor (also known as the Ryli constant), and CD is the characteristic size of the printed features (or Critical dimension). It can be seen from equation (1) that the reduction in the minimum printable size of the feature can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA, or by reducing the value of k ₁ .

In order to shorten the exposure wavelength and thus reduce the minimum printable size, it has been proposed to use extreme ultraviolet (EUV) radiation. The EUV radiation is electromagnetic radiation having a wavelength in the range of 5 nm to 20 nm (for example, in the range of 13 nm to 14 nm). It has further been proposed to use EUV radiation having a wavelength of less than 10 nanometers (e.g., in the range of 5 nanometers to 10 nanometers, such as 6.7 nanometers or 6.8 nanometers). This radiation is called extreme ultraviolet radiation or soft x-ray radiation. By way of example, possible sources include a laser generating plasma source, a discharge plasma source, or a source based on synchrotron radiation provided by an electronic storage ring.

One possible way to enable the use of diffraction-based metrology in EUV systems is to use phase shift patterned devices. The phase shifting patterning device includes a trench (or other phase shifting feature) that produces a phase shift in the redirected beam to deflect the radiation beam off-axis. The degree of phase shift (and therefore the degree of deflection) depends on the degree of defocus. The resulting target can include: a first structure printed via a patterned device feature having no trenches, and thus printed on a non-independent position on the substrate; and a second structure via the trench Patterned device The feature is printed and thus printed on the substrate at a position that is dependent on the focus. In this way, the position of the second structure (relative to the first structure) is focus dependent. However, this configuration may not be desirable because it may require a patterned device that is complex and difficult to manufacture.

The metrology method proposed herein uses an interlaced scatterometer to overlay a modified version of the target for dual patterning overlay measurements. The modified target is a combination of the interleaved stack target and the focus calibration mark described above.

Figure 7a shows an interlaced scatterometer stack target 700 comprising alternating first structures 705 and second structures 710. Both the first structure 705 and the second structure 710 are not intentionally dependent on each other. Specifically in this example, the printed line asymmetry of the first structure 705 and the second structure 710 is not focus sensitive. Of course, there will always be some focus dependence in the formation of any feature (eg, the profile of the feature will change depending on the focus), which is precisely the reason why focus control is significant in the lithography process.

Figure 7b illustrates a DBF target 715 configured for diffraction-based focus (DBF) measurements. It includes a plurality of DBF structures 720, each of which includes a high resolution substructure 725. The high resolution substructure 725 on top of the base pitch produces an asymmetric resist profile for each DBF structure 720, with the asymmetry being dependent on the focus. Thus, the metrology tool can measure the asymmetry from this DBF target 715 and translate this asymmetry into the scanner focus.

Although the DBF target 715 implements a diffraction-based focus measurement, it may not be suitable for use in all situations. The thickness of the EUV resist film is significantly less than the thickness of the EUV resist film used to wet the lithography, which makes it difficult to extract accurate asymmetry information from the asymmetric profile of the structure forming part of the target. In addition, such structures may not comply with strict design constraints that apply to certain product structures. During the device fabrication process, all features of the pattern of the patterned device should be printed and with subsequent processing steps. Device manufacturers use design rules as a way to define feature design to help ensure that printed features meet their program requirements. One such design rule is related to the allowable size of the structure. Another such design The rule is the pattern density, which defines the density of the resulting resist pattern to be within a specific range.

The pattern density is closely related to the degree of defect, since the polishing and diffusion steps may require some degree of uniformity to avoid defects. This situation is significant, for example, in a spacer procedure in which a thin layer is deposited over the resist features, and wherever the resist edge was once present, the program steps reduce the features to a small line. . Achieving a minimum pattern density requirement after the spacer procedure means that it is not possible to use a large feature because only the resist edge is transferred to the substrate as a thin line. In this regard, the DBF structure 720 of the DBF target 715 can be too large. Therefore, in order to increase the spacer pattern density, it may be necessary to increase the number of edges of the resist pattern.

The metrology feature should also follow these design rules as it may otherwise become a source of defects. Therefore, the metrology target should consist of small features that still produce signals that can be detected by the metrology tool given the limits of the given wavelength and capture angle. For DBF target 715, the resulting pattern density after the interval procedure can be significantly too small.

Figure 7c illustrates a modified target 730 in accordance with an embodiment of the present invention. Target 730 includes a first structure 740 and a second structure 750. The first structure 740 is not focus dependent and is substantially similar to the first structure 705 of Figure 7a. The second structure 750 includes a high resolution substructure 760 and a low resolution substructure 770. The high resolution substructure 760 should have a width of less than 200 nanometers so as not to be detected by the scatterometer as an individual structure. In various embodiments, the high resolution substructures 760 can each have a width of less than 100 nanometers, less than 50 nanometers, or less than 25 nanometers. In an embodiment, both the high resolution substructure 760 and the low resolution substructure 770 may have similar CDs; for example, the low resolution substructure 770 may be only 10 nm to 40 nm wider than the high resolution substructure 760. .

The effect of the high resolution of substructure 760 is that substructure 760 is only printed on the substrate when the radiation beam used to print target 730 is within the best focus region. Substructure 760 (or portions thereof) is not printed outside of the best focus area (i.e., when the beam is out of focus). Therefore The form of the printed second structure 750 is dependent on the focus of the radiation beam. This is in contrast to the objects caused by the phase shifting reticle described above, for which the position of the second structure, rather than the form, is focus dependent. In this way, more conventional patterned devices can be used without the need for trenches or similar features for changing the phase.

The change in form of the second structure 750 can manifest itself as a shift in the center of gravity (CoG) of the second structure 750, which can be detected by the scatterometer as pupil asymmetry. The CoG shift can be calibrated against the programmed focus offset substrate. By exposing a substrate with a known focus shift, we can calibrate the behavior of the designed target based on focus (as detected by a scatterometer). The result is a curve similar to curve 1100 in FIG. With this calibrated curve applied, the substrate can be exposed with the best focus, and the scatterometer response can be compared to curve 1100 to determine the focus position for each measurement on the substrate.

Additionally, the presence of the first structure 740 between the second structures 750 increases the pattern density compared to the IDBF target 715.

Figure 7d shows a target 730' comprising a first structure 775 and a second structure 750, both of which are focus dependent, since both of them comprise a high resolution substructure 760 and low Resolution substructure 770. The focus dependence of the first structure 775 is different from the focus dependency of the second structure 750 for the following reasons: the high resolution substructure 760 is tied to the first structure 775 on one side of the low resolution substructure 770, and for The second structure 750 is on the opposite side of the low resolution substructure 770. In this manner, the CoG shift via focus for the first structure 775 and the second structure 750 will be in the opposite direction.

The targets 730, 730' exhibit a high resolution substructure 760 comprising a plurality of high resolution rods each having a similar line width (approximately 15 nm to 25 nm; for example, 22 nm), and It extends in the same direction as the first structure 740 and the low-resolution sub-structure 770. However, other configurations are possible.

FIG. 8 shows details of an additional configuration of an example of the second structure 750. In each case, a single instance of the first structure 810, 810' and the second structure 850, 850', 850" is shown. The manufacturing target is repeated several times in a manner similar to that shown in Figure 7c or in the example of Figure 8(d) in a manner similar to that shown in Figure 7d.

Figure 8(a) shows a second structure 850 that is similar to the second structure 750 except that the high resolution substructure 860 varies in resolution (line width), away from the low resolution substructure 870. Go from lower resolution to higher resolution. This situation provides an incremental variation in the form of the second structure 850 via focus, in that a small defocus would mean that only the high resolution substructure 860 with the highest resolution would fail to print, where high resolution could not be printed. The number of degree substructures 860 increases as the degree of defocus increases. This means that depending on the degree of defocus, there are several different focus dependent forms that the second structure 850 can take, and thus there are several possible centers of gravity shifts in the second structure 850. The minimum high resolution substructure of the high resolution substructure 860 can be as narrow as the narrowness allowed by the resolution of the lithography apparatus.

In one embodiment, the width of the high resolution substructure 860 varies between 15 nanometers and 25 nanometers. The high resolution substructures 860 can each have different line widths or can include adjacent substructures having the same line width. For example, although the high resolution substructure 860 can be configured in a reduced order of line width (as described in the previous paragraph), this configuration can include some (eg, the two thinnest) neighboring high resolutions having the same line width. Degree structure 860.

Figure 8(b) shows a second structure 850' comprising a horizontal substructure 860' that extends in a direction perpendicular to the direction of the low resolution substructure 870. The second structure 850' is substantially identical to the DBF structure 720 in Figure 7b. These structures show a line end (tip to tip) focus response to the CoG shift that produces the second structure 850'. Since all horizontal substructures 860' have the same CD at the patterned device, the right side of the line ends are "pull back" according to defocus, such that the length of each substructure 860' varies with defocus: the defocusing degree Large, each horizontal substructure 860' will be shorter.

Depending on the application, there may be advantages when having a vertical substructure or a horizontal substructure. One substructure or another substructure may be sensitive to program changes, dose changes, or specific aberrations. Expressed as close as possible to the actual product (with focus and aberration sensitivity) At the time of the target design, we may consider any of the designs illustrated in Figure 7 or Figure 8, or any other design within the scope of the claimed patent.

Figure 8(c) shows a second structure 850 comprising substructures 860", the substructure 860" essentially combining the concepts of substructures 860 and substructures 860'. The second structure 850" comprises a two dimensional array of substructures 860" Substructure 860" is configured such that the width of each substructure 860" is reduced in the horizontal direction. This configuration can potentially produce product-like aberration sensitivity.

Figure 8(d) shows a second structure 850 that is substantially similar to the second structure illustrated in Figure 8(a), the second structure 850 being adjacent to the first structure 810' comprising the high resolution substructure 880. The high resolution substructure 880 is similar to the high resolution substructure 860, but is disposed in the opposite direction (thick to thick compared to thick to thin). The high resolution substructure 880 is also on the opposite side of the low resolution substructure 890 as compared to the high resolution substructure 860 versus the low resolution substructure 870.

9 shows the best focus f ₀ and having a second printing type configuration of FIG. 8 (a) shows the 900 950a of the target, and the divergence of the different printing power and having a second configuration 950b, 950c, 950d of Targets 910, 910', 920, 920', 930, 930'. Target 900 causes all high resolution substructures 960 to be printed, even those with the highest resolution. Resolution sub-structure of the target 910 and 910 '(wherein each of the reference system the best focus f ₀ having the same magnitude but with a different sign of defocus of the print) having a second structure 950b, where 960 is less high print. This pattern is repeated for targets 920, 920' and targets 930, 930'; in each case, as the magnitude of the defocus increases, the number of printed high resolution substructures 960 decreases.

Figure 10 illustrates the center of gravity shift between (a) the printed second structure 950a of the target 900 and (b) the printed second structure 950c of the target 920 (or 920'). In each case, the top pattern shows the actual printed objects 900, 920, while the bottom pattern shows that the scatterometer checking each target 900, 920 effectively "sees" after modeling/analysis of the actual scatterometry signal. The approximation of the matter (ie, detection). In the bottom pattern, you can see that the second Structures 950a, 950c are considered by the scatterometer to be effective structures 1060, 1060c having a width dependent on the number of printed high resolution substructures 960. In FIG. 10(a), the center of gravity of the first active structure 1060 (refer to the corresponding first structure 1040) as seen is labeled x. In Figure 10(b), the center of gravity of the second active structure 1060c as seen can be seen to be not equal to x.

The center of gravity shift can be detected by the scatterometer as the asymmetry between the positive and negative diffraction orders of the diffracted radiation. Thus, the detected asymmetry is an indication of the focus, and thus, by using a scatterometer to measure the asymmetry, the focus of the target to be printed can be determined. The asymmetry of the target will affect the diffraction pattern used for the corresponding positive and negative diffraction steps. If there is no asymmetry in the target, the positive and negative diffraction steps will have the same spectral profile. The analysis of the difference between the spectral components of the positive and negative diffraction orders can be used to determine the asymmetry of the target. The phrase "positive diffraction order and negative diffraction order" refers to any of 1 diffraction order and high diffraction order. The diffraction order includes a zero order (specular reflection) that is neither positive nor negative, and then includes a higher order that is conveniently referred to as a complementary pair of positive and negative. Non-zero orders can be referred to as high order. Therefore, +1 order and -1 order are examples of positive and negative orders, and +2 and -2, +3 and -3 are also examples of positive and negative orders. Examples will be described with reference to +1st order and -1st order, without limitation.

Figure 11 is a plot 1100 of the asymmetry or center of gravity on the y-axis and the focus on the x-axis to illustrate how to obtain focus sign information. In Figure 9, it can be seen that the targets 920 and 920' and the targets 930 and 930' are also indistinguishable when the print targets 910 and 910' are indistinguishable. For each pair, the amount of defocus is the same, but the sign is different. This uniqueness issue means a method for extracting focus sign information. The method includes deliberately defocusing the substrate with a known offset such that all focus values are on one side of the peak of the plot 1100. For example, a known focus offset would mean that all of the measured focus values are within the region 1110. The known focus offset can then be subtracted from the measured focus value to find the actual focus value with the correct sign.

The proposed method can include a calibration procedure followed by a monitoring and control procedure. Calibration procedure The sequence includes an exposure focus exposure matrix (FEM) substrate, and the high-order asymmetry is measured in accordance with the focus to calculate the focus calibration curve. The FEM substrate can be used as a calibration substrate for a scatterometer. As is known in the art, a FEM substrate includes a substrate that has been coated with a photoresist, and a pattern is exposed to the photoresist in a plurality of combinations of focus shift and exposure shift. The monitoring and control program can include defocusing the exposure monitoring substrate (to obtain sign information as described above), and measuring high order asymmetry. This measured high order asymmetry can then be converted to focus using the focus calibration curve calculated during the calibration procedure.

To determine the calibration curve from the monitoring substrate, several fields can be exposed by stylizing the focus offset (eg, Rx dip). This situation reduces program dependencies.

This method is easier to apply to off-product measurement due to the need to expose the substrate for exposure to defocus. Exposure to deliberately defocused on the product is clearly undesirable. However, the method can be adapted to focus control on a product by providing a target design with patterned device topography utilizing the three-dimensional mask (M3D) effect. The reticle patterning device can be such that during exposure, the product structure is formed in focus, and the target is formed with focus offset and focus misalignment. The reticle patterning device can include M3D features (such as a scattering rod) that are used to produce an M3D induced optimal focus offset to the target relative to product features that are exposed at the best focus. In an embodiment, the M3D feature may comprise the high resolution substructure of the previous embodiment. In the case of considering the best focus offset caused by the M3D effect, such targets having focus dependent M3D features can then be measured and the focus determined in a manner similar to that already described.

Figures 12 and 13 illustrate additional methods for obtaining sign information. In order to understand this approach, it should be understood that the focus response of the interlaced target described above is actually a printed asymmetric line response (which is roughly linear depending on the focus) and an interlaced target design (between the two structural groups) A combination of center of gravity (CoG). This situation is illustrated by Figure 12(a) and Figure 13a. Figure 12(a) is an interlaced target design 1200 as discussed with respect to Figure 8(b) (although this concept applies to any of the other interlaced target designs described herein). Head The label 1200 includes a first structure 1210 and a second structure 1220. The first structure can belong to, for example, any of the forms disclosed herein. The second structure 1220 is shown here as being similar to the DBF structure 720 (Fig. 7b) or the second structure 870 of Fig. 8(b). Curve 1330 of Figure 13a is the resulting signal response (y-axis) via focus (x-axis). This curve 1330 contains the sum of the curve 1310 and the line 1320, the curve 1310 represents the signal response of the focus point due to the CoG shift of the target 1200, and the line 1320 represents the signal of the focus point due to the asymmetry of the second structure 1220. Respond.

It is proposed to solve the problem of the sign 1200 of the target 1200 by combining signals of multiple (interlaced) targets. The uniqueness problem can be addressed by changing, for example, the design properties of the asymmetrical lines while keeping the symmetric line segments placed relative to the asymmetrical lines the same. This target 1230 is illustrated in Figure 12(b). The target includes a fourth structure 1240 that is different in form from the second structure 1220 but that belongs to the same basic design, the differences being related to parameters such as the line width and/or length of the high definition features. The third structure 1250 in the target 1230 (which is substantially identical to the first structure 1210) is placed opposite the fourth structure 1240 in a manner similar to the relative placement of the first structure 1210 and the second structure 1220 in the target 1200.

As can be seen in Figure 13b, the Bossung type behavior of interlaced targets 1200 and 1230 remains similar, as shown by the similarities of curves 1310 and 1340 (where curve 1340 represents the CoG shift due to target 1230). The signal of the focus point responds, while the asymmetrical line content 1350 changes because the form of the fourth structure 1240 is different from the form of the second structure 1220. The resulting focus response curve 1360 is also displayed. In practice, this means that the tops of the different interwoven objects 1200, 1230 will be displaced relative to each other. The uniqueness problem can then be handled by the operation of finding the difference between the asymmetry signals 1330, 1350 as illustrated in Figure 13c - the resulting signal 1360 will be dependent on the Pasang behavior and asymmetry line such as the CoG signal The degree of similarity between the differences in the signals; and/or by making a (multivariate) focus (dose) model of both targets 1200, 1230.

It should be noted that, in principle, the third structure and the fourth structure may not be similar to the first structure and The second structure. In principle, the placement of the third structure and the fourth structure may not be similar to the placement of the first structure and the second structure.

In addition, the optimal focus offset can be pre-selected into the target response by performing an asymmetric structural response and placement optimization process of the interleaved line structure. This design method for the top shift of the cypress is preferred over the method using the M3D effect as described above, since the M3D effect is unpredictable and can be patterned with different patterned devices and traversing The device pattern changes.

This direct method of obtaining positive and negative information (as illustrated in Figure 13c) is more suitable for non-EUV applications (thicker resists) where the asymmetry of the structure is more pronounced. In such thicker resist applications, the main reason for using interlaced targets is to increase the pattern density. In the case of using the sign extraction method as illustrated in Figure 11, the pre-selection of the best focus offset can be used in EUV thin resist applications. However, in principle, the best focus shift method is suitable for any measurement where the best focus is set to optimize the parameters (and therefore also for non-EUV applications). Typical applications can be monitor type applications. For product applications, the user's program is used to determine the best focus setting, and therefore a focus measurement solution that works under user-specified conditions should be designed.

As mentioned above, the DBF target 715 shown in Figure 7b may not meet the pattern density requirements of certain design rules. To increase the pattern density, the target design can be changed by reducing the base pitch or by adding dummy features to the target. However, reducing the base pitch is likely to be infeasible, as this would cause the diffraction order used by the metrology tool to expand beyond the resolution of the current optics. To address this situation, as already described, it is proposed to provide additional structures between DBF structures 720 (such as the first structure 810 in Figure 8). However, printing of such first structures is also difficult because of the high resolution feature 725 that produces an asymmetric resist profile that limits the space available on the patterned device for the first structure. Therefore, different methods for printing the target containing both the profile profile asymmetry and the desired pattern density at the pitch captured by the metrology tool are desirable.

Accordingly, it is proposed to create the second structure 720 and the first structure 810 in two separate exposures without the need for a second patterned device or a second patterned device pattern. This method is illustrated in Figures 14a and 14b.

Figure 14a shows a patterned device 1400 region that includes a main product region 1405 and a cutting region 1410 at the periphery of the main product region 1405 (for clarity, the cutting region 1410 is shown as being more than the main product region 1405 than the cutting region The actual area of 1410 is larger). In the cutting zone 1410, the second structure 1415 is on one side of the main product area. Details of the second structure 1415' and structure 1420 that will actually be printed on the substrate after exposure by the second structure 1415 are also shown. In the cutting region 1410, the first structure 1425 is directly opposite the second structure 1415 on the other side of the main product region 1405. In addition, details of the first structure 1425' and structure 1430 that would actually be printed on the substrate after exposure of the first structure 1425 are shown.

Figure 14b shows how to print a complete structure. It shows the area of patterned device 1400 in a location for exposure on a substrate. It also shows (dotted line) the region of the patterned device 1400' that is used to closely ground to the previous position prior to exposure to the current exposure. When the product is exposed onto the substrate, it is exposed such that the scribe line region 1410 on one side of the product region overlaps the dicing region 1410 on the opposite side of the previously exposed product region. If the second structure 1415 and the first structure 1425 are correctly positioned on opposite sides of the product area on the patterned device pattern and directly opposite each other (only around the y-axis), then the area is during each pair of exposures ( Overlap on the same column (1440). Of course, the second structure 1415 and the first structure 1425 should be positioned such that the individual structures alternate within the overlap region 1440 such that the resulting printed structure 1445 takes the correct form, with the second structure 1415 interlaced with the first structure 1425.

It should be noted that this method involves dark field (negative) exposure as illustrated in the figure (where the dark areas indicate the resist and the resulting target is a trench type target). This is because the resist will not continue to exist on the substrate between the structures after the first exposure for the conventional target for forming the second structure.

Figures 14a and 14b depict the interleaving of a symmetrical structure with an asymmetrical structure and in particular a structure of the form shown in Figure 8(b). However, this method can be used to print any of the target structures disclosed herein. In addition, it is also possible to use the same method to interleave other features and/or smaller feature arrays.

In another embodiment, the first structure can be a dummy structure. In this configuration, the dummy structure is not used to produce a CoG shift as described above, and focus measurement is only taken from the asymmetry of the second structure. The resulting printed structure having such dummy structures will have both the desired pattern density and the asymmetric profile at the pitch within the capture window of the metrology tool. The dummy structure can take any form (eg, a very high resolution multiple line between each pair of second structures).

The use of this method for increasing the density of the pattern is not limited to DBF metrology, but can be applied to any metrology feature used to increase the density of the pattern, and, for example, any metrology feature using a particular imaging effect printed to relax the pitch. .

Most broadly, this section discloses a method of printing a compound structure via one or more patterned devices or patterned device patterns, wherein the method includes performing a first exposure on a substrate, wherein the first exposure comprises Printing a first printed structure from a first patterned device structure on a first patterned device or a first patterned device pattern; and performing a second exposure on a substrate, the second exposure being adjacent to the first Exposing and causing an overlap region of the first exposure and the second exposure on the substrate, the overlap region comprising the first printed structures, wherein the second exposure is included in the overlap region on the substrate A second patterned device structure on the first patterned device or first patterned device pattern or on a second patterned device or second patterned device pattern prints a second printed structure, thereby forming the compound structure.

The patterned device or patterned device pattern can include a product area and the product One of the perimeter regions of the region, and the first patterned device structures and the second patterned device structures may be located in the scribe region of the patterned device or patterned device pattern, or at a different patterning The scribe line area of the device or patterned device pattern. The first patterned device structure can be located at a first side of the scribe lane region, and the second patterned device structure can be located on a side opposite the first side of the product region such that the first The patterned device structure is positioned to directly face the second patterned device structures relative to a single axis.

Also disclosed is a patterned device comprising a product region and a scribe region at a periphery of the product region, the patterned device further comprising a first patterned device structure, and the scribe line located in the patterned device a second patterned device structure in the region; the first patterned device structure is located at a first side of the scribe region and the second patterned device structure is located opposite the first side of the product region On the side, the first patterned device structures are positioned to directly face the second patterned device structures relative to a single axis.

Although the embodiments are described with respect to EUV lithography, the embodiments herein are applicable to lithography procedures that use radiation at other (eg, longer) wavelengths (eg, at 193 nm).

Although reference may be made specifically to the use of lithography devices in IC fabrication herein, it should be understood that the lithographic devices described herein may have other applications, such as manufacturing integrated optical systems, for magnetic domain memory. Lead to detection patterns, flat panel displays, liquid crystal displays (LCDs), thin film heads, and more. Those skilled in the art should understand that in the context of the content of such alternative applications, any use of the terms "wafer" or "die" herein may be considered as the more general term "substrate" or "target portion". Synonymous. The substrates referred to herein may be processed before or after exposure, for example, in a coating development system (a tool that typically applies a resist layer to a substrate and develops a exposed resist), a metrology tool, and/or an inspection tool. . Where applicable, the disclosure herein may be applied to such and other substrate handlers With. Additionally, the substrate can be processed more than once, for example, to create a multilayer IC, such that the term "substrate" as used herein may also refer to a substrate that already contains multiple processed layers.

Although the use of embodiments of the present invention in the context of the content of optical lithography may be specifically referenced above, it will be appreciated that embodiments of the present invention may be used in other applications (eg, imprint lithography), and in the context of content When allowed, it is not limited to optical lithography. In imprint lithography, the configuration in the patterned device defines the pattern produced on the substrate. The patterning device can be configured to be pressed into a resist layer that is supplied to the substrate where the resist is cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterned device is removed from the resist to leave a pattern therein.

As used herein, the terms "radiation" and "beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (eg, having or being about 365 nm, 355 nm, 248 nm, 193 nm, 157). Nano or 126 nm wavelengths) and extreme ultraviolet (EUV) radiation (eg, having a wavelength in the range of 5 nm to 20 nm), and particle beams (such as ion beams or electron beams).

The term "lens", as the context of the context allows, can refer to any or a combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components.

Although the specific embodiments of the invention have been described above, it is understood that the invention may be practiced otherwise than as described. For example, the invention can take the form of a computer program containing one or more sequences of machine readable instructions describing a method as disclosed above; or a data storage medium (eg, a semiconductor memory, disk or optical disk) ), which has this computer program stored in it.

The above description is intended to be illustrative, and not restrictive. Therefore, it will be apparent to those skilled in the art that the present invention may be modified without departing from the scope of the appended claims.

810‧‧‧ first structure

810'‧‧‧ first structure

850‧‧‧Second structure

850'‧‧‧Second structure

850"‧‧‧ second structure

860‧‧‧High-resolution substructure

860'‧‧‧ horizontal substructure

860"‧‧‧substructure

870‧‧‧Low-resolution substructure

880‧‧‧High-resolution substructure

890‧‧‧Low-resolution substructure

Claims (59)

A method of obtaining focus information related to a lithography process, the method comprising: illuminating a first target, the first target comprising alternating first structures and second structures, the second structures being in a form of focus dependent Having its form dependent on the focus of the patterned beam used to form one of the first targets, and the forms of the first structures do not have the same focus dependence as the focus of the second structures; and detecting Radiation scattered by the first target to obtain an asymmetry measure indicative of an overall asymmetry of the first target for the first target, the asymmetry measurement indicating when the first target is formed The focus of the patterned beam, wherein a patterned device is used to generate the patterned beam, the patterned device including first structural features for forming the first structures and for forming the second structures a second structural feature, wherein: the first structural features and the second structural features comprise low resolution substructure features for forming a low resolution substructure; and the second structures Encourazing that the first structural feature in the case where the form of the first structure is in focus depends on forming a high-resolution sub-structure feature of the high-resolution sub-structure such that the first target is high The number and/or size of the resolution substructures is dependent on the focus of the patterned beam when the first target is formed, wherein the high resolution substructures comprise a two dimensional array of high resolution substructures. The method of claim 1, wherein the form of the first structures does not intentionally depend on the focus of the patterned beam when the first target is formed. The method of claim 1, wherein the form of the first structures is dependent on forming the The focus of the patterned beam at the first target is different from the focus dependence of the second structures. The method of claim 3, wherein the focus dependency is different for the first structure and the second structures, such that a focus shift causes a shift in the center of gravity of the first structure and the second structures, These shifts are in the opposite direction. The method of claim 1, wherein the line widths of the low resolution substructures are greater than the line widths of the high resolution substructures between 10 nm and 50 nm. The method of claim 1, wherein the high-resolution sub-structures comprise a plurality of narrow high-resolution sub-structures extending upward in a direction perpendicular to a direction of the low-resolution sub-structures. The method of claim 1, wherein the high resolution substructures comprise a plurality of narrow high resolution substructures configured parallel to the low resolution substructures. The method of claim 1, wherein the high resolution substructures comprise high resolution substructures having different line widths. The method of claim 8, wherein the high resolution substructures are arranged in an order that reduces line widths from the low resolution substructures. The method of claim 1, wherein the high resolution substructures each have a line width of less than 50 nm. The method of claim 1, wherein the patterned device includes a reticle effect feature that causes a three-dimensional mask effect such that the first target is formed with an optimal focus, the best focus The best focus offset from one of the product features used on the patterned device. The method of claim 11, wherein the reticle effect characteristics comprise one or more of the high resolution substructures. The method of claim 1, wherein the first target is configured such that the asymmetry measurement comprises a center of gravity shift between the first structure and the second structures a first asymmetry component, and a second asymmetry component caused by the asymmetry of the profiles of the second structures, and wherein the first target is formed with an optimal focus, the best The focus is derived from one of the product features used on the patterned device, the best focus offset being caused by the second asymmetry component. The method of claim 13, further comprising optimizing the optimal focus offset via a change in the second structural profile and the relative placement of the first structures and the second structures. The method of any one of claims 1 to 4, further comprising illuminating at least one second target, the second target comprising a third structure and a fourth structure, the fourth structures having a different structure than the second structure At least one parameter. The method of claim 15, wherein the placement of the third structures in the second target relative to the fourth structures is similar to the first structures in the first target relative to the second structures Place. The method of claim 15, further comprising: detecting radiation scattered by the second target to obtain a second asymmetry measure for the second target; determining the second asymmetry measurement from the first The difference between the asymmetry measurements of a target; and the difference is used to determine the sign of a focus decision. The method of claim 15, further comprising: constructing the multi-variable focus model of the first target and the second target; and using the model to determine the sign and/or value of a focus determination. The method of claim 1, further comprising forming the first target in at least two exposures, the forming comprising: performing a first exposure on a substrate, wherein the first exposure comprises forming the first a structure or the second structure; and performing a second exposure on the substrate, the second exposure being adjacent to the first exposure and causing an overlap region of the first exposure and the second exposure on the substrate, The overlap region includes the formed first structure or the formed second structure, wherein the second exposure comprises forming the first structure or the other of the second structures in the overlap region on the substrate In one case, the first target is formed thereby. The method of claim 19, wherein the first structures and the second structures comprise trenches in the photoresist. The method of claim 19, wherein the patterned device comprises a product region and a scribe lane region at a periphery of the product region, and the first structural features and the second structural features are located in the scribe lane region. The method of claim 21, wherein the first structural features are located at a first side of the scribe lane region, and the second structural features are located on a side opposite the first side of the product region such that The first structural features are positioned to directly face the second structural features relative to a single axis. The method of any one of claims 1 to 4, further comprising using the asymmetry measure to determine a focus of the patterned beam of light used to form the target. The method of any one of claims 1 to 4, further comprising performing a calibration procedure and a monitoring and control procedure. The method of claim 24, comprising: during the calibration procedure, using the patterned beam to form the first target by exposing a calibration substrate using a plurality of combinations of focus offset and exposure offset, wherein Performing the illumination and detection on the calibration substrate, and the illuminating and detecting includes obtaining the plurality of the asymmetry measurements according to the focus; and the method further comprises measuring and corresponding to the plurality of the asymmetry measurements Focus offset to calculate a focus calibration curve. The method of claim 25, comprising: during use of the monitoring and control program The patterned beam forms the first target by exposing a monitoring substrate, wherein the illumination and detection are performed on the monitoring substrate; and the method further comprises using the focus calibration curve to convert the asymmetry measurement To a focus measurement. The method of claim 26, wherein the monitoring substrate is exposed with an intentional focus offset, the intentional focus offset being sufficient such that all of the focus measurements are on one side of one of the peaks of the focus calibration curve; And the method further includes calculating the actual focus measurement as one of the focus measurements obtained using the focus calibration curve and the intentional focus offset. The method of claim 26, wherein the focus measurements are used to optimize focus settings during subsequent lithography procedures. The method of any one of claims 1 to 4, wherein the asymmetry measurement comprises calculating a difference between the detected positive high diffraction order and the negative high diffraction order. The method of any one of claims 1 to 4, wherein the patterned beam has a wavelength in the range of 5 nm to 20 nm. The method of any of claims 1 to 4, further comprising: using a patterned beam to form the target as part of a lithography procedure. A patterned device comprising a first pattern for patterning a light beam to form a first target, the first target comprising alternating first and second structures, wherein the patterned device comprises: for forming First structural features of the first structures; and second structural features for forming the second structures, wherein the second structural features are configured such that the forms of the second structures are in focus, Having its form dependent on the focus of the patterned beam when the first target is formed, and the first structural features are configured such that the forms of the first structures do not have the focus of the second structures Dependence of the same focus, Wherein: the first structural features and the second structural features comprise low resolution substructure features for forming a low resolution substructure; and the second structural features and the first structures are The first structural feature in the case where the form is in focus dependence comprises a high resolution substructure feature for forming a high resolution substructure such that the number of high resolution substructures in the first target is and/or The size is dependent on the focus of the patterned beam at the time the first target is formed, wherein the high resolution substructure features comprise a two dimensional array of high resolution substructure features. The patterned device of claim 32, wherein the first structural features are configured such that the form of the first structures does not intentionally depend on the patterned beam when the first target is formed focus. The patterned device of claim 32, wherein the first structural features are configured such that the form of the first structures is dependent on the focus of the patterned beam when the first target is formed, the focus The dependency is different from the focus dependence of the second structures. The patterned device of claim 34, wherein the first structural features are configured such that the focus dependencies are different for the first structures and the second structures such that a focus shift causes the first The structure and one of the second structures are shifted in center of gravity, the shifts being in opposite directions. The patterned device of claim 32, wherein the high resolution substructure features comprise a plurality of elongated high resolution substructure features extending in a direction perpendicular to a direction of the low resolution substructure features. A patterned device as claimed in claim 32, wherein the high resolution substructure features comprise a plurality of narrow high resolution substructure features arranged parallel to the low resolution substructure features. The patterned device of claim 32, wherein the plurality of high resolution substructure features comprise high resolution substructure features having different line widths. A patterned device as claimed in claim 38, wherein the plurality of high resolution substructure features are arranged in an order decreasing the line widths from the low resolution substructure features. The patterned device of claim 32, wherein the high resolution substructure features each have a line width of less than 50 nanometers. The patterned device of claim 32, comprising a product feature and a reticle effect feature, the reticle effect feature causing a three-dimensional mask effect such that the first target is formed with a best focus, the best focus Is the best focus offset for one of these product features. The patterned device of claim 41, wherein the reticle effect features comprise one or more of the high resolution substructures. A patterned device as claimed in claim 32, operable to pattern a beam of light to form the first target in accordance with a lithography procedure. The patterned device of claim 32, comprising a product area and a scribe line area at a periphery of the product area, wherein the first structural features and the second structural features are located within the scribe line area, the A structural feature is located at a first side of the scribe line region, and the second structural features are located on a side opposite the first side of the product region such that the first structural features are positioned relative to one A single axis is directly opposite the second structural feature. The patterned device of claim 44, wherein the patterned device includes a second pattern for patterning a light beam to form a second target, the second pattern comprising a third structural feature and a fourth structural feature, The fourth structural feature has at least one parameter that is different from the second structural features. The patterned device of claim 45, wherein the placement of the third structural features in the second pattern relative to the fourth structural features is similar to the one in the first pattern And placing the first structural feature relative to the second structural feature. A substrate comprising a first target having alternating first and second structures, wherein: the first structure and the second structure both comprise a low resolution substructure; and at least the The second structure includes a high resolution substructure, the number and/or size of the high resolution substructures in the first target being determined by forming a focus of the patterned beam of one of the first targets, wherein The high resolution substructure contains a two dimensional array of high resolution substructures. The substrate of claim 47, wherein the high resolution substructures comprise a plurality of elongated high resolution substructures extending in a direction perpendicular to a direction perpendicular to the low resolution substructures. The substrate of claim 47, wherein the high resolution substructures comprise a plurality of narrow high resolution substructures configured parallel to the low resolution substructures. The substrate of any one of claims 47 to 49, wherein the high resolution substructures comprise high resolution substructures having different line widths. The substrate of claim 50, wherein the high resolution substructures are arranged in an order decreasing the line width from the low resolution substructure. The substrate of any one of claims 47 to 49, wherein the high resolution substructures each have a line width of less than 50 nm. The substrate of any one of claims 47 to 49, wherein the first target is formed using the patterned device of any one of claims 32 to 46. The substrate of any one of claims 47 to 49, comprising a monitoring substrate for monitoring one of the lithography procedures. The substrate of any one of claims 47 to 49, further comprising at least one second target, the second target comprising a third structure and a fourth structure, the fourth structure having Different from at least one parameter of the second structure. The substrate of claim 55, wherein the third structures in the second target are placed relative to the fourth structures in a manner similar to the first structures in the first target relative to the second structures Place. A lithography apparatus operable to perform the method of any one of claims 1 to 31. A computer program comprising a sequence of machine readable instructions, such as the method of any one of claims 1 to 31. A data storage medium storing a computer program such as claim 58.